I. Field of the Invention
This invention relates generally to computer band printers and more specifically to a method and apparatus for generating continuous position pulses during the passage of a missing pulse on the printing band adjacent to the detector.
II. Description of the Prior Art
Computer operated high speed band printers must maintain complete synchronization between the mechanical position of each of the characters on a moving belt and the plurality of hammers which impact with the character for producing the printed lines. A proven solution to this problem involves placing timing marks at each character position along the timing belt. The location of each character is identified with reference to a start or reference position denoted by the absence of a timing mark. This missing pulse is known as the home position. While this system solves the problem of providing a reference pulse, the solution is not without problems. For example, as the missing pulse proceeds around the timing belt at fast speeds, additional electronics are required to generate a timing pulse at the proper position and time when the missing pulse is adjacent to the detector.
Various prior art systems have been developed for generating a pulse at this home position by averaging the time differential between adjacent timing marks and then generating the missing timing mark based upon this average of previous values. However, this solution does not account for instantaneous or relatively fast variations in the speed of the belt which regularly occur during normal operation. Errors in the timing of the missing pulse are displayed as a lateral offset in the characters printed responsive to the missing pulse.
The prior art discloses several different systems of speed control and position measurement. See for example the disclosures of Favard in U.S. Pat. No. 3,795,852, Baker et al in U.S. Pat. No. 3,317,804, Willis in U.S. Pat. No. 3,277,357, Bin-Lun Ho in U.S. Pat. No. 3,217,170, Tomek in U.S. Pat. No. 3,135,903, and Raymond in U.S. Pat. No. 3,117,266.